A number of systems are known for multiplexing a plurality of television signals onto a single transmission means, for example, a cable; multiplexing of television signals can be performed either by frequency multiplexing television signals, i.e., choosing different respective carriers for being modulated by the respective television signals, and transmitting the carriers over a single transmission means. Alternatively, the television signals can be time-division multiplexed, which means chopping the signals up into very small incremental intervals, and transmitting these incremental intervals in a time-division multiplexed manner. This can, in turn, be done either by analog means, or by converting the signals into digital signals, and reconverting the digital signals into analog signals at the monitor-receiver.
The multiplexing methods of the prior art are all costly and complex, and in particular require a bandwidth which is usually a multiple of the bandwidth required for a single television channel, and at least equal to n times the bandwidth of a single channel, where n is the number of television channels to be transmitted. Although sophisticated bandwidth-reduction methods have been proposed, they have generally not been able to reduce the bandwith significantly. A television system which transmits auxiliary information during the vertical blanking interval of each television field has also been proposed, but such a system is not applicable for selectively choosing one of a plurality of television transmitters for transmitting video signals to the monitor-receiver. This is particularly true where the transmitters relaying the camera-generated video signals all operate on the same radio frequency.
There is also known a television multiplexing system which includes a circuit that inserts a digital coded sync signal and a digital code into a video signal for activation the channel from which the video signal was generated, so that a plurality of signals can be sent over a single hard or dedicated line. The digital sync signal and the digital coded signals are generated by a single crystal controlled clock, so that they are always in synchronism with each other. In demultiplexing the signals, so as to feed the video signal to a proper recording channel, the sync signals are utilized for shifting the digital coded signals into a shift register, and the shift register, in turn, activates a decoder according to the code stored in the shift register for selecting the proper recording disc or receiver for storing the video signal.